This invention relates to couplings for tubes.
The invention is more particularly concerned with a tube coupling of the kind having a collet with resilient arms arranged to co-operate with a cam surface on a member surrounding the collet, which member has an internal surface tapering in one axial direction and engaging the arms of the collet so that the fingers are forced inwardly by axial movement of the collet in one direction. With such a tube coupling, the end of the tube may be pushed into the coupling through the collet from the end thereof remote from the arms. Any outward pull on the tube with respect to said member surrounding the collet tends, by the engagement between the collet and the tube, to pull the collet in the direction to remove it from said member and thereby causes the arms, by engagement with the cam surface, to grip the tube more tightly. Provided the coupling is of the appropriate size to fit the tube, if a tube is inserted in the collet, the inward movement of the arms is restricted and hence the collet cannot be withdrawn outwardly from said member. This arrangement thus gives a form of coupling in which the end of the tube can be inserted directly into the coupling and is engaged thereby in a manner which prevents withdrawal of the tube merely by any pull thereon. The tube can be released however by pushing the collet inwardly into said member whilst pulling the tube outwardly; thus release can only be effected by a deliberate action and not by accidental pull on the tube.
It is an object of the present invention to provide an improved form of tube coupling of this kind. In considering the problems with prior types of constructions, it is convenient to refer to the end of the collet having the arms as the inner end and the other end of the collet as the outer end; the arms thus extend from a point along the length of the collet towards the inner end. In prior types of coupling, the taper on the cam surface, which taper is such that the diameter reduces from the inner end towards the outer end, has necessitated that the collet should be inserted into the member forming the cam surface from the inner end of that memer. This then leads to the requirement that the main body of the coupling must be formed in two parts so as to permit the assembly of the collet into a part having the required cam surface and then the securing of this member into a main part of the body. Also, since the collet has to be assembled into the member with the cam surface from the inner end thereof, the maximum diameter of the base of the collet, that is to say the part towards the outer end, must not exceed the minimum diameter of the aforementioned member having the cam surface. One is thus led to a construction in which the main body is formed in two parts. In one form of construction, such as that shown for example in U.S. Pat. No 3,454,290, these two parts can be threaded one on to the other so that they can be separated by being unscrewed when it is required to obtain access to the collet to enable a tube to be withdrawn. If the two parts of the body are secured together after the collet has been assembled in the cam surface member, then release of a tube from the coupling can only be effected by ensuring that the collet protrudes outwardly from the body. However this part of the collet, as explained above, must not have any portion of greater diameter than the minimum diameter of the cam surface member. In practice this means that the end of the collet is a relatively thin cylinder, as for example in the constructions of U.S. Pat. No. 3,653,689, thereby raising problems in applying axial pressure to this collet when a tube is to be released. It is possible, as shown in U.S. Pat. No. 3,743,326, to swage the outer end of the collet radially outwardly thereby increasing its diameter but this results in the collet being permanently secured onto the member surrounding it, so preventing dismantling of the assembly.